For medical tomographic images such as CT images or MRI images, tomographic images having an image matrix size of 512×512 pixels are utilized as standard images. In conjunction with recent medical image resolution enhancement, tomographic images of high resolution having an image matrix size of 1024×1024 pixels or 2048×2048 pixels have been obtainable.
Since such resolution enhancement was not assumed conventionally, there is a possibility that tomographic images of 1024×1024 pixels cannot be applied due to the capacity of a Picture Archiving and Communication System (PACS), etc., and merely images having image matrix information of 512×512 pixels can be archived. A method for compressing an image of high resolution to an image of 512×512 pixels may be adopted, but the method may sacrifice the resolution. Accordingly, it is necessary to extract and store a partial region of an image having image matrix information of 512×512 pixels from an image having image matrix information of 1024×1024 pixels or 2048×2048 pixels. In this case, an original image of the extracted image may not be specified.